The Portugal international, who represented the Red Devils between 2003 and 2009, has stressed that the Premier League leaders will pose a stern test, but has insisted that his side is superior.
"I believe things will go well. In my opinion Real Madrid have a better team, but we have to show that on the pitch because United are a very united team and always have been in recent years," the attacker told UEFA's official Champions League magazine.
"They're a team that always do well, every year they're at the top and therefore a team we respect a lot. It will be an extremely difficult match, especially in Manchester.
"The game at Old Trafford will be a match in which I will feel a lot. I was there for six years. I have a lot of friends there, people I will see with great pleasure, it will be a match with a lot of emotions."
The first leg is scheduled to take place at the Santiago Bernabeu on Feb. 13.